1. Field of the Invention
The present invention relates to a surface mount type condenser or capacitor, which is mounted on a substrate and is mainly used as a noise filter.
2. Description of the Related Art
Reduction in the size of an electronic power supply has rapidly been developed accompanied by an advancement of high-performance, a downsizing, and a reduction in the weight of electronic parts in recent years.
The reduction in the size of the electronic power supply can be achieved by increasing the operational frequency of the power supply to a high frequency level. However, requirements for the performance of electronic parts used for an electronic power supply circuit employing such power supply, particularly, the performance of a noise filter surface mounted on a substrate, i.e., a condenser has become more and more strict. As a surface mount type condenser capable of meeting such strict requirements for the performance, an aluminum solid electrolytic condenser employing an electro-conductive functional polymer as a cathode and surface mounted on a substrate has been developed and brought into practical use.
Compared with a conventional aluminum condenser or tantalum condenser, this aluminum solid electrolytic condenser is advantageous in that the equivalent series resistance thereof is 1/20 through 1/50 of that of the above-mentioned conventional aluminum or tantalum condenser.
FIG. 1 is a cross-sectional view of the conventional constitution of a surface mount type condenser.
As shown in FIG. 1, conventional surface mount type condenser has such a constitution that two substantially planar-plate shape cathodes 2 sandwich a first metallic plate 7 in the shape of a planar plate. Two cathodes 2 are vertically connected to one another at the sides thereof.
Therefore, respective faces of cathodes 2, which are not in contact with first metallic plate 7 form surfaces of two cathodes 2, and one of such surfaces, i.e., a surface 2a is connected to cathode terminal 4, and opposite ends of first metallic plate 7 projecting from between two cathodes 2 forms two anodes. On the respective ends of these anodes are formed two anode terminals 5, which are connected, respectively, to lands 11 arranged on substrate 6.
Further, in order to prevent occurrence of short-circuiting of cathodes 2 (cathode terminals 4) and anodes 3 (anode terminals 5), either electrical insulation layers are provided on the surfaces of anodes 3 and anode terminals 5 or surface mount type condenser 1 per se is sealed by insulating resin.
Accordingly, when this surface mount type condenser 1 is mounted on substrate 6, direct current containing noise inputted from one of anode terminals 5 is filtered, and the direct current component only is output to the other of anode terminals 5.
However, with the conventional surface mount type condenser, in a high frequency region equal to or more than 10 MHz, such a phenomenon conspicuously occurs that a part of noise input in one of the anode terminals is transmitted as an electromagnetic wave in the air so as to arrive at the other of the anode terminals. Namely, when such phenomenon occurs, since signals input in one of the anode terminals is transmitted as an electromagnetic wave (noise) in the air to short-circuit to the other of the anode terminals, it is difficult to thoroughly remove noise in the signals. This fact means that in the high frequency region equal to or more than 10 MHz, sufficient removal of noise could not hitherto achieved.
Taking into consideration the above-described problems encountered by the prior art, an object of the present invention is to provide a surface mount type condenser capable of preventing transmission of electromagnetic wave between anode terminals and being excellent in its noise removal performance in a high frequency region.
A surface mount type condenser according to a first invention of the present patent application, provided for solving the above-described problems of the prior art, comprises: two anode portions; two anode terminals connected to respective of the two anode portions in a manner of confronting a substrate; two planar plate-shape cathode portions; a first substantially planar plate-shape metallic plate sandwiched by the two cathode portions and including the two anode portions; a cathode terminal connected to one of the cathode portions in a manner of confronting the substrate; and a second substantially planar plate-shape metallic plate electrically connected to a surface of the other of the cathode portions and arranged in a manner of covering predetermined regions of the anode terminals.
According to the above-described constitution, when high-frequency electric current is permitted to flow into the surface mount type condenser, an action of electromagnetic wave discharged particularly from the anode terminals can be suppressed between the anode terminals and the second metallic plate.
At this stage, the second metallic plate is provided not for interrupting the passage of the electromagnetic wave so as to prevent transmission of the electromagnetic wave between the two anode terminals but for electrically suppressing the action of the electromagnetic wave by an arrangement in which the second metallic plate electrically connected to the cathode portions having electrolyte confronts the anode terminals.
Accordingly, an occurrence of short-circuiting of the electromagnetic wave in the air due to transmission of the electromagnetic wave between the two anode terminals can be cancelled, and an appropriate removal of noise by the surface mount type condenser can be effected, so that noise can be more efficiently removed in the case of high frequency range.
Further, the above-mentioned predetermined regions indicate regions of the anode terminals, which should be covered by the second metallic plate when the second metallic plate is arranged for covering portions of the anode terminals to an extent such that the action of the electromagnetic wave can be electrically suppressed.
A surface mount type condenser according to a second invention of the present patent application comprises a substantially planar plate-shape second metallic plate connected to a surface of the other of the cathode portions and having a surface thereof confronting the surfaces of anode terminals.
According to the above-described constitution, a phenomenon of short-circuiting of electromagnetic wave in the air, namely transmission of the electromagnetic wave between the two anode terminals can be decreased.
At this stage, the second metallic plate of this constitution may be arranged to confront the surfaces of the anode terminals in compliance with an arrangement requested by the function of the surface mount type condenser.
Namely, at least a portion of the surface of the second metallic plate may be arrange to confront a portion of the surfaces of the anode terminals. Hereby, a decrease in a space necessary for the installation of the surface mount type condenser, and reduction in the manufacturing cost thereof can be achieved.
A surface mount type condenser according to a third invention of the present patent application comprises a substantially planar plate-shape second metallic plate connected to a surface of the other of the cathode portions and having a surface thereof confronting the whole of surfaces of the anode terminals.
According to this constitution, the electromagnetic wave discharged from the surfaces of at least two anode terminals can be suppressed by the confronting surface of the second metallic plate having an area equal to or greater than those of the surfaces of the anode terminals, so that appropriate removal of noise can be achieved by the surface mount type condenser, and further the removal of noise in the high frequency range can be more efficiently achieved.
A surface mount type condenser according to a fourth invention of the present patent application is characterized in that the second metallic plate has a surface thereof provided with a layer of magnetic material formed thereon.
According to this constitution, the magnetic field that generates for the reason that the positive polarization (the anode portions and the anode terminals) and the negative polarization (the cathode portions and the cathode terminal) of the surface mount type condenser are of a common phase, is rendered difficult to change its magnetic flux due to provision of the magnetic material layer. As a result, the noise can be damped. Namely, the noise generating in the positive and negative polarizations at the same electric potential, i.e., the so-called common mode noise can be damped.
A surface mount type condenser according to a fifth invention of the present patent application is characterized in that the width of the layer of magnetic material is set to be equal to or larger than that of the first metallic plate.
According to this constitution, since the width of the magnetic material layer is set on the basis of the width of the first metallic plate, the magnetic material layer is formed in a manner such that the layer covers over the first metallic plate, and therefore can surely and efficiently damp the common mode noise.
Further, when a direction in which the first metallic plate projects against a dielectric is defined as an X-direction, the afore-mentioned width of the layer corresponds to the length in a direction orthogonal to the X-direction in an identical plane.
A surface mount type condenser according to sixth and seventh inventions of the present patent application is characterized in that the second metallic plate is extended in a manner of covering side faces of the anode portions.
According to this constitution, the anode terminals and the second metallic plate formed so as to cover over these anode terminals suppress, from the side, the action of the electromagnetic wave discharged from the anode terminals to thereby suppress transmission of the wave between the anode terminals, thus, appropriate removal of noise can be achieved.
A surface mount type condenser according to eighth through tenth inventions of the present patent application is characterized in that both of the mutually confronting surfaces of the second metallic plate and the anode portions are provided with the insulating layer formed thereon, respectively.
According to this constitution, the second metallic plate electrically connected to the cathode portions and the anode terminals are prevented from being electrically short-circuited.
Particularly, even if the second metallic plate and the anode portions (the first metallic plate) were deformed by any stress acting thereon, the provision of the insulating layer can surely insulate the second metallic plate from the anode portions and the anode terminals.
A surface mount type condenser according to eleventh through thirteenth inventions of the present patent application is characterized in that the space through which the second metallic plate and the anode terminals confront is filled with insulating resin.
According to this constitution, electrical insulation is provided between the second metallic plate and the anode terminals by the insulating resin, and the strength of the metallic plate as well as those of the anode terminals and portions, namely the strength of the surface mount type condenser per se can be increased.
More specifically, protection can be provided for a certain kind of member or members liable to be deformed by any stress, such as the second metallic plate and the anode portions (the first metallic plate).
A surface mount type condenser according to fourteenth through sixteenth inventions of the present patent application is characterized in that the whole surround containing the space through which the second metallic plate and the anode terminals confront, is sealed by the insulating resin.
According to this constitution, not only prevention of electric short-circuiting within the surface mount type condenser per se and an increase in the strength thereof but also protection of the second metallic plate and firm fixing of the surface mount type condenser to the substrate on which diverse components are mounted, can be accomplished.
As will be understood from the foregoing description, according to the surface mount type condenser in accordance with the present invention, as the second metallic plate is electrically connected to the cathode portions, and is disposed so as to confront respective of the anode terminals to which electromagnetic wave noise is transmitted, the action of the electromagnetic wave can be suppressed. Therefore, the electromagnetic wave noise which is liable to be discharged into the air can be selectively damped, and accordingly the noise removal performance in the high frequency range equal to or more than 10 MHz can be appreciably increased.
The above and other objects, features and advantages of the present invention will become apparent from the following description, based on the accompanying drawings, which illustrate examples of preferred embodiments of the present invention.